This application claims the priority of Application No. 100 08 189.4, filed Feb. 23, 2000, in Germany, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device and a method for testing a tank ventilation system having a tank ventilation valve in a motor vehicle.
It is known to open and close selectively the tank ventilation valve of a tank ventilation system for testing its operability. The motor reactions to the opening and closing of the tank ventilation valve are then examined, for example, if the speed and the air mass change when opening and closing the tank ventilation valve. In past systems, however, it is only known to compare each operating datum by itself with a threshold value in order to test the operability of the tank ventilation system.
Depending on how fast an idle controller reacts, however, to the changes made by opening and closing the tank ventilation valve, different reactions result. In the case of a slow idle controller the result will be predominantly a reaction in the speed. In the case of a fast idle controller, the result will be predominantly a reaction in the air mass. Moreover, all reactions in between, where both the speed and the measured and preset air mass change, are also, of course, possible. In total, this means that the respective reaction is highly dependent on the application. In the event that the speed and the air mass change simultaneously, the amplitudes of each individual signal may vary widely. This state leads altogether to a poor signal-to-noise ratio.
The object of the present invention is to provide a device and a method for testing a tank ventilation system. The device and method allow an accurate and flawless test of its operability independent of the applications of an idle controller.
This and other objects and advantages are achieved by the testing method and apparatus according to the invention, in which each respective individual variable (operating datum) is not compared with its own threshold value. Rather the different changes of the individual variables are combined into a total reaction, which is then evaluated. In the evaluation one can then apply a well-known method of comparison with a threshold value.
In the case of the inventive device and the inventive method, one may proceed from the hypothesis that in the case of an idling engine the respective air masses and speeds are approximately proportional (n˜ml). One assumes in particular that, when the tank ventilation valve is closed, the quotient resulting from the air mass and speed is approximately constant (ml0: n0 is approximately constant).
Usually the air mass, which is additionally supplied by way of the tank ventilation valve, is not measured or specified. Therefore, when the tank ventilation valve is opened, more air is made available to the engine than is preset by way of the idle controller. Thus, the total air mass with the tank ventilation valve open is derived from the measured air mass (ml) and the air mass mlTEV, flowing in additionally by way of the tank ventilation valve.
In place of an air mass (ml), measured with an air flow sensor, the preset air mass nominal value (ml_nominal) of the idle controller may also be used as the air mass signal. This feature is especially advantageous if the measured air mass value cannot be resolved finely enough or if it varies too much. Naturally the use of the air mass nominal value is also suitable as the air mass signal when there is no air flow sensor.
In an advantageous embodiment, a relative change in the air mass is computed from the air mass and the engine speed when the tank ventilation valve is opened and from the air mass and the speed when the tank ventilation valve is closed. The relative air mass can be calculated, on the one hand, from a difference of the quotient resulting from the engine speed for an opened tank ventilation valve and the engine speed for a closed tank ventilation valve, and, on the other hand, from the quotient resulting from the air mass with the tank ventilation valve open and the air mass with the tank ventilation valve closed.
The methods disclosed in the patent claims are suitable for operating the device, according to the invention.